This invention relates to methods for applying coatings to volatile gelatinous surfaces on substrates in a high vacuum, and more particularly this invention relates to thin film deposition of dielectric on liquid crystal on a substrate with specific application to deposition of multilayer optical quality dielectric materials on polymeric liquid crystal materials for use in electro-optic applications.
One of the challenges of manufacturing is the difficulty of vacuum coating of materials that have a tendency to evaporate and decompose under vacuum. One material of interest is polymer dispersed liquid crystal (PDLC) film, the material used in electro-optical modulators to image large surfaces.
The known method for EO modulator fabrication is use of commercial NCAP (nematic curvilinear aligned phase) material in which PDLC is sandwiched between two layers of ITO Mylar® polyester film. The conventional manufacturing process involves lamination of a film to a laminate of NCAP. Two patents, assigned to Photon Dynamics, Inc., describe such processes:
“Modulator Transfer Process and Assembly,” Michael A. Bryan, U.S. Pat. No. 6,151,153 (2000).
“Modulator Manufacturing Process and Device,” Michael A. Bryan, U.S. Pat. No. 6,211,991 B1 (2001).
The lamination process has the limitation of inconsistent surface flatness, mechanical instability, and extremely low yield in manufacture.
Concurrent techniques under development involve the lamination of a polyester film having a mirror coating onto a layer of light sensitive but volatile material and spin coating processes. (See U.S. patent application 10/685,687 filed concurrently entitled METHOD FOR FABRICATING ELECTRO-OPTIC LIGHT MODULATOR in the names of Xianhai Chen, David Baldwin, and Alexander Nagy, and U.S. patent application 10/686,367 filed concurrently entitled METHOD FOR MANUFACTURING PDLC-BASED ELECTRO-OPTIC MODULATOR USING SPIN COATING in the name of Chen and Nagy). While the mirror surface directly engages the light sensitive material, representing an improvement over prior art techniques, the assembly process is subject to human-introduced errors such as wrinkling of the pellicle, nonuniform adhesion, capture of dust particles and creation of bumps at the time of assembly. What is needed is a structure and a technique to allow direct vacuum coating of materials, thus eliminating the film lamination process.